This invention relates to a rotary, radially flexible, self-aligning journal for a power takeoff shaft and finds particular utility in conjunction with a geared power takeoff shaft of a gas turbine engine.
Antipollution laws have created grave problems with respect to the continued use of internal combustion reciprocating engines. An alternative to reciprocating engines is the inherently low polluting gas turbine engine. A major drawback, however, to the large usage of gas turbine engines is their high cost relative to comparable size reciprocating engines. If such costs could be significantly reduced, gas turbine engines could replace reciprocating engines in many areas.
The assignee of the present application has disclosed a low cost, single shaft, gas turbine engine in U.S. patent application Ser. No. 214,703. One of the outstanding cost-reducing features of that gas turbine engine is the use of powdered metal gears as part of the engine's transmission. Such gears reduce the cost of the transmission to a fraction of that heretofore found in transmissions employing precision machined gears. Utilization of powdered metal gears in the transmission in the initial speed reduction (from approximately 100,000 rpm to approximately 13,500 rpm) is believed to be facilitated by the provision of a radially flexible journal for the power takeoff shaft adjacent the driving gear. The radially flexible journal permits omnidirectional movement of the power takeoff shaft, and accordingly the driving gear, thereby permitting the driving and driven gears to move radially relative to one another in response to variations in tooth form and gear eccentricity. It is believed that the relative gear movement improves gear life by lessening the dynamic and peak tooth loads and accordingly allows the use of a lower class of gear to transfer power from the turbine rotor. Further, in the disclosed gas turbine engine, the radially flexible journal can be tuned to dampen shaft vibrations and thereby remove critical shaft vibrations from the operating range of the engine. However, in some operational environments, the disclosed radially flexible journal has been observed to allow excessive power takeoff shaft centerline excursion, resulting in a reduction in shaft dampening, undesirable vibrational inputs to the shaft, and compressor and/or turbine blade rubbing.
It is accordingly an object of the present invention to provide a radially flexible, low excursion journal for a gas turbine power takeoff shaft subjected to a unidirectional radial force.
It is a further object of the present invention to provide an improved, low cost transmission having a relatively low class driven gear in meshing engagement with a relatively high speed, low class driving gear that will rotate with minimal centerline excursion.